svn commit: r366378 - head/sys/vm

[Mark Johnston]

Author: markj
Date: Fri Oct  2 19:04:09 2020
New Revision: 366378
URL: https://svnweb.freebsd.org/changeset/base/366378

Log:
  uma: Use LIFO for non-SMR bucket caches
  
  When SMR was introduced, zone_put_bucket() was changed to always place
  full buckets at the end of the queue.  However, it is generally
  preferable to use recently used buckets since their items are more
  likely to be resident in cache.  So, for buckets that have no constraint
  on item reuse, use a last-in-first-out ordering as we did before.
  
  Reviewed by:	rlibby
  Tested by:	dhw, glebius
  Sponsored by:	The FreeBSD Foundation
  Differential Revision:	https://reviews.freebsd.org/D26426

Modified:
  head/sys/vm/uma_core.c

Modified: head/sys/vm/uma_core.c
==============================================================================
--- head/sys/vm/uma_core.c	Fri Oct  2 19:03:42 2020	(r366377)
+++ head/sys/vm/uma_core.c	Fri Oct  2 19:04:09 2020	(r366378)
@@ -733,7 +733,15 @@ zone_put_bucket(uma_zone_t zone, int domain, uma_bucke
 			zone_domain_imax_set(zdom, zdom->uzd_nitems);
 		if (STAILQ_EMPTY(&zdom->uzd_buckets))
 			zdom->uzd_seq = bucket->ub_seq;
-		STAILQ_INSERT_TAIL(&zdom->uzd_buckets, bucket, ub_link);
+
+		/*
+		 * Try to promote reuse of recently used items.  For items
+		 * protected by SMR, try to defer reuse to minimize polling.
+		 */
+		if (bucket->ub_seq == SMR_SEQ_INVALID)
+			STAILQ_INSERT_HEAD(&zdom->uzd_buckets, bucket, ub_link);
+		else
+			STAILQ_INSERT_TAIL(&zdom->uzd_buckets, bucket, ub_link);
 		ZDOM_UNLOCK(zdom);
 		return;
 	}